If `f:R-R` is defined by `f(x)=3x+4`, then `f(f(x))` is____________.

Answer

To find \( f(f(x)) \) where \( f(x) = 3x + 4 \), we will follow these steps:

### Step 1: Write down the function
We start with the function given:
\[ f(x) = 3x + 4 \]

### Step 2: Substitute \( f(x) \) into itself
To find \( f(f(x)) \), we need to substitute \( f(x) \) into the function \( f \):
\[ f(f(x)) = f(3x + 4) \]

### Step 3: Apply the function to \( 3x + 4 \)
Now, we will apply the function \( f \) to \( 3x + 4 \):
\[ f(3x + 4) = 3(3x + 4) + 4 \]

### Step 4: Distribute and simplify
Next, we distribute the 3:
\[ = 9x + 12 + 4 \]
Now, combine like terms:
\[ = 9x + 16 \]

### Final Answer
Thus, the value of \( f(f(x)) \) is:
\[ f(f(x)) = 9x + 16 \]

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